Oregano (Orignaum sp.) has been used for centuries as a traditional herb, spice and also in traditional medicine. Oregano essential oils are used as ingredients in several applications including tooth paste, mouth wash, gums etc. The main active molecules in oregano essential oil are carvacrol and thymol. These molecules have been shown to have potent antimicrobial activity1 and have been used as feed additives to improve gastrointestinal health in farm animals. Oregano essential oils in animal feed diets have been shown to improve growth and reproductive performance in pigs2,3 and overall performance in broilers. Oregano oil is also used in several personal care applications. Thymol is also used as a biological control of Varroa mites in bee hives.
Accumulation of essential oil in oregano and other herbs varies with the developmental stage of the plant4. The highest carvacrol and thymol content in Orignaum onites was found at the pre-flowering stages5. However another study reported highest carvacrol and thymol content during the post flowering and seed formation stages in mid-June6.
The bio active molecules, although controlled genetically, are strongly affected by environmental influences of a particular growing region; and also by agronomic conditions, harvesting time and the type of processing4. The age of the plants at the time of harvest seems to affect the oil yield and composition. Total thymol and carvacrol content of oregano oils obtained from younger plants was higher than that of the mature plants4. The amount of water received by the plant did not have a significant effect on the thymol and carvacrol content of the oil extracted from Mexican oregano7.
The effects of temperature and duration of day light on the bioactive components of oregano essential oil have been studied. Oregano plants, like many other species, grown under higher temperatures, light intensity and longer day length periods tend to have increased oil content8. The harvest time was crucial to maximize the essential oil yield and the concentration of its main components in oregano. Carvacrol and thymol content were generally much higher during summer months8.
While progressive genetic improvement was focused on increasing the essential oils, little or no effort has yet been made in the improvement of oregano for better production of carvacrol, thymol or other antimicrobial or antioxidant molecules. Extraction of thymol from a hyper-accumulating oregano clonal line is crucial for economically viable commercial thymol production. Therefore developing oregano varieties with high levels of thymol combined with high biomass will provide an economically valuable thymol source.